Sql problem, pivot question?

Question

Hi guys,
I have an interesting problem and do not manage to find a sollution.
I need to create a report, and we call it variance/trending report. let me explain.
I have a table that holds all employess with their salaries, every month.
currenly my selects gets all employess with their salaries from current and previous month. and the result looks like:
Employee_iD| Salary| month
1          |500   |   C
2          |100   |   P
1          |650   |   P
3          |100   |   p
3           |180   |   C
how can I do my select so I can see the result, in different columns, in a manner in which I can compare the salaries between them (from current and previous month):
Employe_iD| current_month| previous_month | variance
1        |500                 | 650                 | -150
2        |                      | 100                 |
3        |180                 |100                   |80you can see that C, measn current month, and P measn previous month.
I think I will have data in my select for both, previous and current. If not, I will treat it as zero.
I gave a simple exemple . My select is a little more complex.
any help is appreciated.
Thanks

Answer 1

May be..
SQL> WITH tbl AS (SELECT 1 empid,500 sal,'C' mon FROM DUAL UNION ALL
  2               SELECT 2 empid,100 sal,'P' mon FROM DUAL UNION ALL
  3               SELECT 1 empid,650 sal,'P' mon FROM DUAL UNION ALL
  4               SELECT 3 empid,100 sal,'P' mon FROM DUAL UNION ALL
  5               SELECT 3 empid,180 sal,'C' mon FROM DUAL
  6               )
  7  SELECT empid,NVL(MAX(DECODE(mon,'P',sal)),0) previous_sal
  8              ,NVL(MAX(DECODE(mon,'C',sal)),0) current_sal
  9              ,NVL(MAX(DECODE(mon,'P',sal)),0)- NVL(MAX(DECODE(mon,'C',sal)),0)
10                var
11  FROM tbl
12  GROUP BY empid          
13               ;
     EMPID PREVIOUS_SAL CURRENT_SAL        VAR
         1          650         500        150
         2          100           0        100
         3          100         180        -80